In the case where particulate articles or liquid-soaked articles, such as pickles, which tend to spill are to be packaged by an automatic packaging machine using bags which are unstable as compared with flat-bottomed self-standing bottles or cans, the essential condition is to clamp, suspend and stabilize the bag so that it will not fall down, as in the case of the packaging machine disclosed in U.S. Pat. Nos. 3,982,376 or 4,027,450. In said known packaging machine, a number of equispaced clamps are installed on an endless chain supported on two chain wheels, said clamps being circulated integrally with the chain by the driving force of said chain wheels, and along said chain there are installed a mechanism for feeding a bag to each clamp, a mechanism for opening the bag supported by the clamp, a mechanism for filling an article into the bag and a mechanism for sealing the opening in the bag filled with the article; thus, an article tending to spill can be automatically packaged in an unstable bag.
The aforesaid full automatic packaging machine could be relatively easily provided with a vacuum packaging function. This provision could be made, for example, by supporting on a chain a number of pressure resistant containers adapted to be opened and closed and enclose said clamps, conveying said pressure resistant containers by said chain, successively closing said pressure resistant containers between the mechanism for filling an article into each bag and the mechanism for sealing the opening in the filled bag, and successively sucking out the air in the pressure resistant containers. With the packaging machine adapted to perform bag feeding operation, bag opening operation, filling operation, evacuating operation and sealing operation along the endless track as described above, however, it takes a considerable time to reduce the pressure in the pressure resistant container from the atmospheric pressure to a vacuum, during which time the pressure resistant container will travel a considerable distance along the endless track, making it necessary to correspondingly prolong the endless track, thus entailing a disadvantage that the packaging machine is increased in size.
The present invention has for its object the provision of a vacuum packaging method which makes it possible to shorten the endless track and reduce the size of the packaging machine.